The present invention relates to an optical disc for recording information with data recording densities of a plurality of kinds, an optical disk recording-reproducing apparatus and an information recording-reproducing method.
In optical discs capable of recording a large capacity with a high density, a further increase in capacity is being promoted by increasing the number of recording layers. For example, in the Blu-ray discs (BD), approaches such as use of four layers each having a standard data recording density 25 GB/layer and use of three layers each having a higher density 33 GB/layer are made in order to record information of 100 GB on one sheet of disc. When optical discs which differ in recording format including the data recording density thus appear, an optical disc apparatus which discriminates the recording format and conducts recording and reproducing so as to correspond to the recording format becomes necessary.
As a technique relating to this, a configuration which changes over an optical system (numerical aperture NA) according to the kind of the disc and changes characteristics of the signal processing system so as to be linked to the changeover is disclosed in, for example, JP-A-09-282785. A structure which records format information of a plurality of recording layers in a read-in area in order to identify the format of respective recording layers in the case where one sheet of disc has a plurality of recording layers recorded using different formats is disclosed in JP-A-2007-26617.